1. Field of the Invention
This invention relates in general to variable capacity vane compressors for air conditioning systems, particularly for vehicles.
2. Description of the Prior Art
One type of automotive air conditioning compressor in use is a variable capacity vane compressor. In this type of compressor, a compression housing has a chamber that is oval in shape. A cylindrical rotor rotates within the chamber. The rotor has radial vanes mounted to it which slide in slots formed in the rotor. Refrigerant at suction pressure enters the compression chamber. The vanes compress the refrigerant, which passes outward through a valve.
The compressor demand varies according to speed and atmospheric conditions. At highway speed, the demand is usually lower than while idling on a hot day. To vary the capacity, a rotary valve disk or plate mounts in engagement with a shoulder on the compression housing. The valve plate has lobes on its perimeter which will change the position of the opening from the suction chamber into the compression chamber, depending upon the rotational position of the valve plate.
U.S. Pat. No. 5,364,235 shows a linearly moving actuator which will rotate the valve plate to selected positions depending upon changes in the discharge and intake pressures. A control valve supplies a control pressure to one side of the actuator, and the other side of the actuator is at intake pressure. The control valve operates in response to varying intake and discharge pressures.
The linear actuator has a spring which urges the actuator away from the intake side toward the control pressure side. The spring will position the actuator in the minimum delivery position when the compressor is not operating. Tests have shown that pressure surges sometimes occur, causing the actuator to move rapidly from the minimum delivery to the maximum delivery position. This rapid shift in position has disadvantages.
U.S. Pat. No. 5,364,235 also discloses a pressure chamber for applying an axial force on a rotary valve plate that is proportional to the control pressure. The annular pressure chamber is located in a recess that contains a seal. The seal applies a force to a bearing pack which in turns engages the valve plate. In the '235 patent, the bearing pack components are located partially within a recess in the valve plate, and partially within a portion of the valve housing. While workable for applying the desired pressure to the valve plate, this arrangement results in assembly difficulties.